Need Upgrading Advice

[tt189]

Currently I have;

Opteron 175 socket 939
ASUS A8N32-SLI Deluxe NF4SLI 939
HD 320G Seagate sata
1gbx2 Corsair TWINXMS
512mbx2 Corsair TWINXMS
EVGA GeForce 8800 GTS Superclocked 640MB GDDR3
OCZ GameXStream 700w
Windows XP

I'm thinking of upgrading to Intel, need some advice on a cpu, Mobo, and Ram.

Budget;
~$200 for a cpu
~$200 for a Mobo
~$150 for Ram

The primary function will be a gaming PC, for games like First person shooters, Real Time strategy, and MMORPGs.

Any suggestions would be helpful.